The goal of this work is to understand sound transmission through normal, diseased and reconstructed middle ears so that better diagnostic tests and surgical procedures can be offered to patients with middle-ear disease. Middle-ear diseases such as chronic otitis media and otosclerosis, which affect over 10 million people in the US, are common causes of significant conductive hearing loss. The current battery of diagnostic tests (otoscopy, audiometry, tympanometry) cannot reliably differentiate ossicular pathology, especially when the tympanic membrane is intact or if there has been prior middle-ear surgery. Additionally, it is commonly acknowledged that post- operative hearing results after tympanoplasty procedures for chronic otitis media are often unsatisfactory. Factors contributing to the modest nature of surgical results include lack of clear understanding of the critical structure-function relationships in the reconstructed ear, and failure of current diagnostic tests to determine such relationships. Laser Doppler vibrometry has been demonstrated to be more sensitive than audiometry and tympanometry in assessing middle- ear function, because the laser spot (only 100 micrometers diameter) can be focused at various points on the tympanic membrane and malleus, and because vibrometry is unaffected by the ear canal (unlike tympanometry). We propose to use vibrometry, other acoustical measurements (admittance and reflectance), audiometry and tympanometry to investigate structure-function relationships in (a) normal ears, (b) diseased ears with ossicular pathologies, and (c) reconstructed ears that have undergone surgery for chronic otitis media or otosclerosis. Similar vibrometry and acoustical measurements will also be made in a surgically-modified human temporal bone preparation that mimics diseased and reconstructed ears. Our approach should lead to a better understanding of the structure-function relationships in normal and pathological middle ears, improved differential diagnosis of middle-ear lesions, better pre-operative patient counseling and surgical planning, optimization of surgical techniques and hearing results, and reduction in the number of failed surgeries.